It has heretofore been a practice to manufacture the disc head slider for computer by machining ferrite materials in block form. However, since the ferrite material is low in its high frequency permeability, its input for recording and output for reading will be low when it is used as the magnetic head in a thin film magnetic circuit or at the time of high speed writing and reading of data. In recent years, however, general trend in this field of technology is such that inductance of the disc head is so reduced as to enable the disc head to be operated in a higher frequency region, and also a gap width is made so small as to improve its high speed writing and reading as well as its recording density.
Further, as has been observed in the recent trend in this field of technology, manufacture of the disc head in a thin film form has been positively and progressively undertaken in keeping up with increase in the recording density. As consequence of this, more and more stringent requirements have been imposed on the characteristic properties of the substrate materials for the thin film magnetic head, and there have been demands for development of those materials satisfying the undermentioned required characteristics.
(1) Crystal grains constituting the materials are so fine, uniform, and dense that they do not permit presence of micro-pores therein.
(2) The materials are excellent in their affinity with the recording medium, their sliding property, and their wear-resistant property.
(3) The materials have good machinability; that is to say, they have high speed machinability and are excellent in their precision machinability.
(4) The materials have good affinity with those materials to be coated on their surface.
In order to meet these demands, there have been developed a material for the ceramic substrate member for the thin film magnetic head suitable for high density recording, which is principally composed of aluminum oxide and titanium carbide (vide: Japanese Patent Kokai Publication No. 60-66403, etc.), and a composite material produced by forming a partial solid-solution of titanium nitride with titanium carbide. Besides the abovementioned components, there is added to aluminum oxide MgO, CaO, NiO or the like which are effective as the grain growth inhibitor or the sintering aid.
In such thin film magnetic head, particular requirements are such that not a single micro-pore should be present in the surface part of the substrate when it is subjected to the ultra-precision mirror surface finishing, and that the substrate has good precision machinability.
Therefore, with a view to rendering the substrate, which has been finished to have an ultra-precision mirror surface, to be free from such micro-pores, it is necessary that a mixture of powders for the substrate material is sintered to its theoretical density, and yet the bonding among the ceramic crystal grains is sufficiently strong so as to form a fine micro-structure. On the other hand, however, machinability of such ceramic sintered body is very poor.
In order therefore to solve this problem, there has been developed a material which is composed principally of, for example, aluminum oxide and titanium carbide, 5 parts by weight or less of a machinability agent such as MgO, NiO, etc. being added to 100 parts by weight of such principal component (vide: Japanese Patent Kokai Publication No. 57-135772).